diff --git a/bitcoin/Cargo.toml b/bitcoin/Cargo.toml
index 7afb1864..3714b2fe 100644
--- a/bitcoin/Cargo.toml
+++ b/bitcoin/Cargo.toml
@@ -10,6 +10,7 @@ categories = ["cryptography::cryptocurrencies"]
 keywords = [ "crypto", "bitcoin" ]
 readme = "../README.md"
 edition = "2021"
+rust-version = "1.56.1"
 exclude = ["tests", "contrib"]
 
 [features]
diff --git a/fuzz/Cargo.toml b/fuzz/Cargo.toml
index b897bdfb..9abf5cd6 100644
--- a/fuzz/Cargo.toml
+++ b/fuzz/Cargo.toml
@@ -1,6 +1,7 @@
 [package]
 name = "bitcoin-fuzz"
 edition = "2021"
+rust-version = "1.56.1"
 version = "0.0.1"
 authors = ["Generated by fuzz/generate-files.sh"]
 publish = false
diff --git a/fuzz/generate-files.sh b/fuzz/generate-files.sh
index 39105af4..18cba6a8 100755
--- a/fuzz/generate-files.sh
+++ b/fuzz/generate-files.sh
@@ -12,6 +12,7 @@ cat > "$REPO_DIR/fuzz/Cargo.toml" <<EOF
 [package]
 name = "bitcoin-fuzz"
 edition = "2021"
+rust-version = "1.56.1"
 version = "0.0.1"
 authors = ["Generated by fuzz/generate-files.sh"]
 publish = false
diff --git a/hashes/Cargo.toml b/hashes/Cargo.toml
index ef2619d9..a68a0a70 100644
--- a/hashes/Cargo.toml
+++ b/hashes/Cargo.toml
@@ -10,6 +10,7 @@ categories = ["algorithms"]
 keywords = [ "crypto", "bitcoin", "hash", "digest" ]
 readme = "README.md"
 edition = "2021"
+rust-version = "1.56.1"
 exclude = ["tests", "contrib"]
 
 [features]
diff --git a/internals/Cargo.toml b/internals/Cargo.toml
index 56247424..ade1a5d6 100644
--- a/internals/Cargo.toml
+++ b/internals/Cargo.toml
@@ -10,6 +10,7 @@ categories = ["cryptography::cryptocurrencies"]
 keywords = ["internal"]
 readme = "README.md"
 edition = "2021"
+rust-version = "1.56.1"
 exclude = ["tests", "contrib"]
 
 [features]